1. Field of the Invention
The present invention relates generally to improved dental compositions for treating the pulp and root canals in a tooth. The compositions contain a mixture of particulate materials such as calcium silicate, calcium aluminate, calcium hydroxide, and hydroxyapatite; various organic water-soluble polymeric materials; and surfactants that interact with the polymeric materials.
2. Brief Description of the Related Art
The inner portion of a tooth includes a pulp cavity that contains soft living tissue or the “pulp” of the tooth. The pulp includes connective tissue, blood vessels, cells, and nerve endings. The pulp cavity comprises an upper pulp chamber and root canals that extend to the apex or apical section of the tooth deeper into the jaw. The outer (visible) portion of the tooth is referred to as the crown and has a covering of enamel. The hard enamel protects softer dentinal tissues in the upper portion of the tooth. The enamel consists of a hard, calcium-based substance, hydroxyfluorapatite. The dentin tissue contains a matrix of minute hydroxyapatite tubules interspersed with collagen fibers that surround and protect the tooth pulp. The outer (non-visible) portion of the tooth root is covered with cementum, a thin hard tissue that joins the root to the surrounding bone through Sharpey's fibers. Dental decay, or caries, is caused by bacteria accumulating on teeth and forming a biofilm (plaque). The biofilm produces acids that dissolve and weaken the hydroxyapatite of the tooth, thereby causing decay.
When dental caries are found in the enamel portion of a tooth, a dental professional will remove the caries to prevent further decay of the tooth. Then, the cavity is “filled” with a composite resinous material or amalgam filling. However, in some instances, the dental caries may be so deep that it penetrates to the dentin tissue. At this point, the bacteria and other microorganisms can migrate rapidly into the pulp tissue causing infection and inflammation. As a result, abscesses or inflammation may form in the pulp, and eventually in the periapical tissues surrounding the root apex. Provided that the dental disease is not too progressed, dental professionals will use root canal treatment procedures to remove the infected tissue from the tooth and replace it with an inert, biocompatible material. Otherwise, extraction of the tooth might be required.
The root canal system of a tooth is complex and many treatment methods can be used depending upon the condition of the patient and approach of the practitioner. In general, root canal treatment methods first involve drilling an opening in the crown of the tooth to provide access to the pulp cavity. Then, endodontic files are used to remove the pulp and clean and shape the root canals. The files are used with an irrigant. After using the files, an irrigant may be used to remove the smear layer created by the files. A sealer is coated on the wall of the root canals and then, the root canals are filled with a filling material. This sealing of the roots ideally prevents bacteria and other microorganisms from re-entering and causing infection of the living tissue surrounding the root tip. As a final step, the pulp chamber and opening in the crown of the tooth is sealed with a dental restoration such as a filling material. Preferably a permanent crown is placed over the opening in the tooth, such crowns being made of metal, porcelain-enameled metal, polymer-veneered metal, or ceramic. A post may be placed in the root for stability of the crown, although this is usually done after the root canal procedure, and before the crown is made.
One method for filling root canals involves using naturally occurring or synthetic gutta-percha, an isomer of rubber. Gutta-percha points having a tapered conical shape can be prepared, and these points can be fitted into the root canal. Historically, one older treatment method involves using single cones of gutta-percha. In this method, zinc oxide-eugenol cement sealer is first placed in the root canal. Then a single unheated cone of gutta-percha is fitted into the root canal. New techniques have been developed including cold lateral compaction, where multiple gutta-percha cones are compressed into the root canal after a root canal sealer is placed on the canal walls. More recently, procedures employing heated gutta-percha are being used that allow the gutta-percha to flow so that it can move into the minute intra-canal spaces, lateral canals, accessory canals, and other irregularities of the canals. One such technique uses a metal or plastic carrier coated with a layer of gutta-percha. The carrier includes a metal or plastic shaft with a distal tapered end that extends from a cylindrically shaped handle. The carrier transports the gutta-percha into the working length of the canal and compacts the gutta-percha into lateral and accessory canals. Once the carrier is stabilized in the canal, the upper handle portion and shaft is severed at a point level to the orifice of the canal using a dental bur or other sharp instrument. The lower portion of the shaft remains in the canal encased in the hardened gutta-percha. Other warm gutta-percha techniques include the compaction of gutta-percha that is extruded into the canal after a root canal sealer is placed. Combinations of cold and warm gutta-percha sealing techniques also can be used.
Other root canal treatment methods involve using portland cement to repair root defects such as iatrogenic perforations, or when apical surgery is performed to fill the root end. In general, portland cement contains a compound formed from calcia, silica, alumina, and iron oxide materials. Portland cement is commonly gray, but white versions, with lower iron content are known. The portland cement is combined with water to form a slurry-like composition that is introduced into the root canal defect. The composition solidifies to seal the canal. When portland cement materials are used to fill or seal the root canals, the cement particulates should have a small particle size. The fineness of a cement is represented by the surface area and one measurement thereof is the Blaine Number representing the ratio of the cement's particle surface area to its weight (square centimeters of surface per gram).
Torabinejad et al., U.S. Pat. Nos. 5,769,738 and 5,415,547 describe using a portland cement composition having a Blaine number in the range of 4,000 to 5,500 cm2/gram for various surgical and non-surgical root canal treatment procedures including sealing root canals, performing apicoectomies, and repairing root canal perforations. The '738 and '547 patents disclose combining the portland cement with water to form a composition that is introduced into the root canal. There is no disclosure in the '738 and '547 patents for making a composition containing water-soluble polymeric materials, surfactants, and portland cement.
In addition to portland cements, other biomedical cements have been developed for medical and dental applications. For example, Lu et al., US Patent Application Publication US 2007/0098811 discloses a biomedical cement containing at least one phosphate compound and at least one calcium silicate compound that does not contain any aluminum or magnesium compounds. Preferably, the cement contains 45 to 80 weight percent calcium oxide; 10 to 35 weight percent silica; and 1 to 30 weight percent phosphate. Water-soluble polymeric materials are not added to the cement. Hydroxyapatite can be added to form hydroxyapatite/calcium silicate hydrate gel in situ at room temperature.
Kawahara et al., U.S. Pat. No. 4,647,600 discloses a dental cement that can be used for pulp-capping, base lining, root canal filling, and other applications. The composition is made of two parts. Part A comprises at least two powders—100 parts by weight of a powder containing calcium oxide and alumina; and 2 to 70 parts by weight of calcium hydroxide powder. According to the '600 patent, it is important that the powder particulates be surface-treated with organic and/or inorganic acids to increase the flowability of the particulate during mixing. Part B comprises an aqueous solution containing 0.01 to 70 wt. % of a water-soluble, high molecular weight substance (for example, polyvinyl pyrrolidone, polyethylene oxide, sodium polyacrylate, and sodium polymethacrylate.) Dental cements containing powder particulate, water-soluble polymeric materials, and surfactants are not disclosed in the '600 patent.
Kawahara et al., U.S. Pat. No. 4,689,080 discloses a composition of alumina cement that can be used in dental pulp capping, root canal filling, sealing, alveolar bone reconstruction, and the like. The alumina cement is an industrial cement that can be mixed with other materials. The composition consists of: a) industrial calcium aluminate powder; b) calcium type powder hardening retarder such as calcium hydroxide, calcium chloride, or calcium oxide; and c) water-soluble polymer such as polyvinyl alcohol, polyvinyl pyrrolidone, gum arabic, acrylic acid, glycerine, sodium metasilicate, low-molecular fatty acid, or hydrophobic natural resin. According to the '080 patent, it is important that a hardening retarder, preferably calcium hydroxide, be added to the mixture. The calcium hardening retarder is added in a ratio of 1-20 parts by weight to 100 parts by weight of alumina cement powder. Compositions containing powder particulate, water-soluble polymeric materials, and surfactants are not described in the '080 patent.
Jefferies and Primus, PCT International Application Publication No. WO 2005/087178 discloses a polymer-infiltrated structure of calcium-based cement that can be potentially used as a pulp capping agent, root repair material, root canal sealer, and other clinical products. A self-etching/self-priming dental adhesive can be applied to the surface of an unset dental cement material to form a polymer-infiltrated structure. The surface infiltration permits stabilization of the cement before it fully sets. In another example, a portland cement material is described as being mixed with a solution of 2-10% polyvinyl pyrrolidone having a molecular weight between 40,000 and 1,300,000. There is no disclosure of using any surfactants in the composition.
Another material that is used in surgical and non-surgical root canal procedures is ProRoot™ MTA root repair material available from Dentsply Tulsa Dental Specialties (Tulsa, Okla.). ProRoot MTA material has a composition similar to portland cement and does not contain any water-soluble polymeric materials. Particularly, the MTA material includes fine hydrophilic particles of dicalcium silicate, tricalcium silicate, tricalcium aluminate, tetracalcium aluminoferrite, calcium sulfate dihydrate, and bismuth oxide that are combined with water to form a cement-like material. The MTA material is available in gray and white colored formulations. The oxides used in the MTA powder are of the highest purity to ensure that no heavy metals are included and used in the body. MTA root canal repair material is used in a wide variety of clinical applications. Particularly, the cement-like material has been used to repair root canal perforations during root canal therapy; fill root ends; treat injured pulps in procedures known as pulp capping and pulpotomy, and repair root resorption.
Although MTA materials are generally effective in surgical and non-surgical root canal procedures, some dental literature has criticized these materials for having poor handling properties and a sand-like feel. There is a need for a composition having improved handling and placement properties. The composition should have good working time so that the dental practitioner can handle and place the material more effectively and preferably the material will start to set before the dental procedure is completed. Ideally, the material should promote the healing or repair of the pulp-tissue or the tissue surrounding root canal tips. The material should also provide a tight seal against the root canal dentin to prevent bacterial migration through the root canal. The present invention provides such improved materials.